A Media gateway controller (MGC) and a media gateway (MG) are two key components in a packet network. The MGC has call control function and the MG has service bearing function, thereby achieving separation of a call control plane and a service bearing plane. In this way, network resources can be shared sufficiently, device upgrading and service expansion can be simplified, and the development and maintenance cost can be reduced dramatically. For example, FIG. 1 illustrates a networking schematic diagram of MG and MGC in the next generation network (NGN). A communication protocol between MGs is the Real-time Transport Protocol (RTP), and communication protocols between MG and MGC that are widely employed currently include the H.248/Gateway Control Protocol (MeGaCo) and the Media Gateway Control Protocol (MGCP). The MGCP version 1 was developed by the Internet Engineering Task Force (IETF) in October, 1999 and was amended in January, 2003. The H.248/MeGaCo version 1 was developed by the IETF and the International Telecommunications Union (ITU) together in November, 2000 and was amended in June, 2003. The H.248 version 2 was developed by the ITU in May, 2002 and was amended in March, 2004. The H.248 version 3 was developed by the ITU in September, 2005.
Taking H.248 as an example, the various resources on the MG are abstracted as terminations. Terminals can be grouped into physical terminations and temporary terminations. The former represent some physical terminations having semi-permanent existence, such as a time division multiplex (TDM) channel, and the later represent some public resources that are applied for temporarily and will be released after use, such as an RTP stream. Further, the MG is overall represented by a root termination. A combination between terminations is abstracted as a context. The context may include a plurality of terminations. Therefore, the association among terminations is described as a topology. For a termination not associated with another termination yet, it is contained in a special context known as Null context.
For such abstract model based on a protocol, a call connection is actually an operation upon the termination and the context. Such operation is implemented by request and response for a command between the MGC and MG. Types of the command include Add, Modify, Subtract, Move, Audit Value, Audit Capability, Notify, and Service Change. Command parameters, also referred to as descriptors, are classified into property, signal, event, and statistic, etc. Parameters indicating service dependency are aggregated into a packet logically.
The H.248 uses local and remote descriptors to negotiate media parameters, wherein a local descriptor defines parameters of a locally received media, and a remote descriptor defines parameters of a remotely received media, such as a receiving address, a receiving port, and a media type, etc. By default, the H.248 uses the session description protocol (SDP) of the Request for Comments (RFC) 2327 developed by the IETF to describe these media parameters in the local and remote descriptors. However, the RFC3266 developed by the IETF additionally is update of the RFC2327 for supporting IPv6, and the IETF amended the SDP in the recently developed RFC4566, causing change of the protocol syntax. When the MGC uses RFC4566 in the call/session control, the MGC is required to use RFC4566 in controlling the MG.
In such a situation, the backward compatibility may not be achieved by a scheme of simply changing the SDP referenced in the H.248 from RFC2327 to RFC4566. Since the existing version negotiation mechanism of the H.248 does not define a negotiation mechanism relating to the SDP version, the existing version negotiation mechanism of the H.248 cannot enable the MGC and MG that do not both support the new RFC4566 to achieve backward compatibility, i.e., falling back to use the old RFC2327.